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Growth measurements of potato (Solanum tuberosum L.) cvs. Norland (NL), Denali (DN), and Kennebec (KN) were taken from 21-day-old plantlets grown in vitro. Studies were conducted in a growth chamber, with nodal explants grown in culture tubes with loose-fitted Magenta 2-way caps containing Murashige and Skoog salts with either 0, 1, 2 or 3% sucrose. The cultures received either 100 or 300 μmol m-2 s-1 photosynthetic photon flux (PPF), and the growth chamber was maintained at either 400 or 4000 μmol mol-1 CO2. All cvs. showed significant increases in growth on 0% sucrose media at 4000 μmol mol-1 CO2, indicating an autotrophic response. At 400 μmol mol-1 CO2, all cvs. showed an increase in total plantlet dry weight (DW) with increasing sucrose under both PPF levels. Within any sucrose treatment, the highest total DW for all cvs. resulted from 300 μmol m-2 s-1 PPF and 4000 μmol mol-1 CO2. At 4000 μmol mol-1 CO2, shoot DW declined with sucrose above 2% for DN and sucrose above 1% for NL at both PPF levels, suggesting that high sucrose levels may hinder growth when CO2 enrichment is used.
Abstract
Potato plants (Solanum tuberosum L. cvs. Russet Burbank, Norland, and Denali) were grown for 56 days in controlled-environment rooms under continuous light at 20C and 50% or 85% RH. No significant differences in total plant dry weight were measured between the humidity treatments, but plants grown under 85% RH produced higher tuber yields. Leaf areas were greater under 50% RH and leaves tended to be larger and darker green than at 85% RH.
Leaf stomatal conductance was monitored with a steady-state porometer throughout growth and development of soybean and potato plants grown at 500, 1000, 5000, and 10,000 (potato only) μmol mol-1 carbon dioxide (CO2). All plants were grown hydroponically with a 12-hr photoperiod and 300 μmol m-2 s-1 PPF. As expected, conductance at 1000 was < 500 μmol mol-1 for both species, but conductance at 5000 and 10,000 μmol mol-1 was ≥ that at 500 μmol mol-1. Subsequent short-term (24-hr) tests with potato and wheat plants grown at 1000 μmol mol-1 showed that raising CO2 to approx. 10,000 μmol mol-1 or lowering CO2 to 400 μmol mol-1 increased conductance compared to 1000 μmol mol-1 for potato, while only lowering CO2 to 400 μmol mol-1 increased conductance for wheat. Furthermore, raising the CO2 to 10,000 μmol mol-1 increased dark-period conductance in comparison to 1000 μmol mol-1 for potato, while dark-period conductance for wheat leaves was low regardless of the CO2 concentration. Results suggest that very high CO2 levels (e.g. 5000 to 10,000 μmol mol-1) may substantially increase water use of certain crops.
Lettuce (cv. Waldmann's Green) and radish (cv. Giant White Globe) plants were grown hydroponically with a 18-hr photoperiod and 300 μmol m-2 s-1 PPF. Treatments consisted of 400, 1000, 5000 and 10000 μmol mol carbon dioxide (CO2). Leaf stomatal conductance was monitored with a steady-state porometer across one diurnal period at 21 days and all plants were harvested at 25 days. Conductance at 400 and 10000 was > 1000 μmol mol-1 for lettuce and conductance at 5000 and 10000 was > 1000 and 400 μmol mol-1 CO2 for radish. Carbondioxide treatments having the lowest leaf conductances also resulted in the highest yields, viz. 1,000 μmol mol-1 CO2 for radish and 5000 μmol mol-1 CO2, for lettuce. Dark-period conductance was higher at 5000 and 10000 μmol mol-1 CO2 compared to 400 and 1000 μmol mol-1 CO2. The higher dark-period conductances were 70% of the light-period rates for lettuce and 30% for radish. Water use efficiency (WUE) (g biomass kg water-1) was lowest at 400 μmol mol-1 CO2 for both lettuce and radish and was highest at 1000 μmol mol-1 CO2 for lettuce and 5000 μmol mol-1 CO2 for radish. The results suggest that WUE was improved with moderate CO2 enrichment but declined at very high concentrations, i.e. 10000 μmol mol-1 for lettuce and radish.
To characterize CO2, exchange, potatoes (Solanum tuberosum cv. Norland) were grown for 90 and 105 days in KSC's Biomass Production Chamber, a 116 m-3 closed cuvette, with 0.5 strength modified Hoagland solution using recirculating NFT culture, 12/12 photoperiod, 1000 μmol mol-1 CO2, and approximately 900 μmol m-2 s-1 PPF from HPS lamps. Canopy gas exchange responses to CO, concentration, light intensity, and photoperiod were experimentally determined. CO, exchange showed a linear response to PPF (up to 1100 μmol m-2 s-1 max.) and a light compensation point of about 150 μmol m-2 s-1. Sustained exchange rates of >45 μmol CO2, m-2 s-1 were obtained 50 days after planting. CO2 saturation was approximately 1200 μmol mol-1 CO2 with a compensation point < 100 μmol mol-1. A dark cycle of less than 4 hours resulted in a rapid, continuous decrease in C02 exchange rate which was partially reversed by a 12-hour dark cycle. There was a weak correlation CO2 exchange and leaf starch concentration at the end of the dark cycle.
Photoperiod treatments were imposed on potato (Solanum tuberosum L. cv. Norland) grown in the Biomass Production Chamber (BPC) at Kennedy Space Center under HPS lamps (670 μmol m-2s-1 PPF) at 1200 μmol mol-1 CO2. Stand A decreased with dark cycle length, which correlated with the change in leaf starch concentration during the dark cycle, but not absolute starch concentration. A series of growth chamber experiments were performed to characterize the effect of photoperiod and PPF on CO2 assimilation and starch mobilization in single leaves. Plants grown on a 12/12 photoperiod at either low (300 μmol m-2s-1) or high (600 μmol m-2s-1) PPF were subjected to short-term photoperiod treatments of 8/16, 16/8, and 24/0 and diurnal CO2 assimilation rates, CO2 response curves, and leaf starch content were determined. CO2 compensation point was not affected by either photoperiod or PPF. However, Amax (when normalized for PPF) decreased with increasing photoperiod. Anet correlated with the changes in specific leaf weight and starch content during the dark cycle.
As humans explore the solar system, life support will need to be increasingly self-sufficient. Growing higher plants and using recycling technologies can improve self-sufficiency. Sodium is an essential mineral for humans, but not typically for plants. Recycling sodium back to humans through food crops may reduce the need for sodium supplements in the human diet. However, if sodium from waste streams is added to the plant system in greater quantities than it is removed, then plant toxic levels may result. The recommended daily sodium requirement is 3000 mg per person. Based on a 20-m2 growing area per person, 150 mg·m–2 sodium would need to be removed each day. Most crops will not remove enough salt when grown at very low sodium levels; however, when grown in 20 mM sodium, plant uptake may meet the 3000 mg/d human sodium requirement without affecting yields. We grew four different salad crops (lettuce, radish, spinach, and table beet) hydroponically and calculated plant uptake rates and partitioning with 0, 20, 40, or 80 mM sodium supplemented nutrient solutions (corresponding to ≈1.4, 4.0, 8.0, and 13.0 dS·m–1 electrical conductivity). Sodium at 40 and 80 mM reduced edible yields. Sodium replaced tissue potassium in most cases, whereas calcium and magnesium concentrations were much less affected, particularly at 20 mM sodium. This data will be used to model sodium flows within a bioregenerative life support system and determine the feasibility of sodium recycling using food crops.
Bean (Phaseolus vulgaris L.) cv. Etna, a dry bean variety, and cv. Hystyle, a snap bean variety, were grown at 400 and 1200 μmol·m-2·s-1 CO2 to determine the effects of CO2 enrichment on plant growth and stomatal conductance. Plants were grown in controlled environment chambers for 70 days at each CO2 level using nutrient film technique hydroponics. An 18-h light/6-h dark photoperiod was maintained for each test, with a corresponding thermoperiod of 28 °C/24 °C and constant 65% RH. Diurnal stomatal conductance measurements were made with a steady-state porometer at 28 days after planting (DAP) and 49 DAP. As expected, plant growth and yield was consistently increased for each cultivar when plants were grown at 1200 μmol·m-2·s-1 CO2 compared to 400 μmol·m-2·s-1 CO2. Stomatal conductance measured during the light period showed an expected decrease for each cultivar when grown at 1200 μmol·m-2·s-1 CO2 compared to 400 μmol·m-2·s-1 CO2. However, during the dark period, stomatal conductance was higher for each cultivar grown at 1200 μmol·m-2·s-1 CO2. These results suggest a stomatal opening effect in the dark when plants are exposed to enriched levels of CO2. Tests are underway to investigate the effects of CO2 levels greater than 1200 μmol·m-2·s-1 on the growth and stomatal conductance of bean.
A wheat (Triticum aestivum cv. Yecora Rojo) stand was grown using nutrient film culture in the closed conditions of NASA's Biomass Production Chamber. Rates of photosynthesis and respiration of the entire stand (about 20 m2) were determined daily using a regime of 20 hr light/4 hr dark, 20 C light/16 C dark an average PPF of 600 μmol/m2/s from HPS lamps, and a CO2 cone of 1000 ppm. Fractional interception of PPF by the stand reached a maximum of 0.96 at 24 days from planting. Rates of photosynthesis were constant throughout the photoperiod as determined by short term drawdowns of CO2 throughout the photoperiod. Drawdown rates of CO2 were correlated with rates determined by logging of mass flow of CO2 injected during chamber closure. Photosynthetic drawdowns of CO2 indicated that photosynthesis was not saturated at 1000 ppm CO2 and that the CO2 compensation point was about 50 ppm. Whole stand light compensation points were 200 to 250 μmol/m2/s between days 13 and 70 and then increased rapidly during senescence.
Radish (Raphanus sativus cv. Giant White Globe) and lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown for 25 days in growth chambers at 23 °C, ≈300 μmol·m-2·s-1 PPF, and 18/6 photoperiod, and four CO2 concentrations: 400, 1000, 5000, and 10,000 μmol·mol-1. Average total dry mass (g/plant) at the 400, 1000, 5000 and 10,000 μmol·mol-1 treatments were 6.4, 7.2, 5.9, and 5.0 for radish and 4.2, 6.2, 6.6, and 4.0 for lettuce. Each species showed an expected increase in yield as CO2 was elevated from 400 to 1000 μmol·mol-1, but super-elevating the CO2 to 10,000 μmol·mol-1 resulted in suboptimal growth. In addition, many radish leaves showed necrotic lesions at 10,000 μmol·mol-1 by 17 days and at 5000 μmol·mol-1 by 20 days. These results are consistent with preliminary tests in which radish cvs. Cherry Belle, Giant White Globe, and Early Scarlet Globe were grown for 16 days at 400, 1000, 5000, and 10,000 μmol·mol-1. In that study, `Giant White Globe' produced the greatest total dry mass at 1000 (3.0 g/plant) and 5000 μmol·mol-1 (3.0 g/plant), and the least at 10,000 μmol·mol-1 (2.2 g/plant). `Early Scarlet Globe' followed a similar trend, but `Cherry Belle' showed little difference among CO2 treatments. Results suggest that super-elevated CO2 can depress growth of some species, and that sensitivities can vary among genotypes.